(Field of the Invention)
The present invention relates to a slip control device which is provided in an electric automobile such as a vehicle running by drive of only a motor or a vehicle including both a motor and an engine, and which performs torque control when a slippage occurs during running with the motor, to eliminate the slippage.
(Description of Related Art)
In order to prevent acceleration from being decreased due to a slip of a drive wheel caused by an excessive driving torque during acceleration for a vehicle, a traction control device for the vehicle is generally known to detect the slip amount of the drive wheel and limits engine output or a wheel braking force such that the slip amount of the drive wheel reaches a target slip amount for the frictional coefficient of a road surface (e.g., Patent Document 1). In particular, the traction control device controls the slip amount by decreasing the engine output or increasing the braking force.
Patent Document 2 proposes that, if a value of angular acceleration of a drive wheel exceeds an angular acceleration threshold, feedback correction is performed on a torque command by using a torque command correction value ΔTr including an item obtained by multiplying the angular acceleration by a feedback gain. Specifically, grip of the drive wheel on a road surface is detected by comparing the angular acceleration and the angular acceleration threshold. In addition, after the drive wheel returns from the slippery road surface to a normal road surface, a temporary decrease in the angular acceleration is detected by comparing the angular acceleration and another angular acceleration threshold. The values of the angular acceleration threshold and the feedback gain are set in accordance with an accelerator position and the wheel speed of the drive wheel. Moreover, a value of coefficient used in determining the angular acceleration threshold and the feedback gain is changed on the basis of whether a rotation frequency of a motor unit exceeds a base rotation frequency.
In addition to the above, an electric automobile which performs slip control and includes an in-wheel motor drive device including a wheel bearing unit, a motor unit, and a reducer unit, has been proposed, in which a disturbance observer is provided, which determines an estimate of an external force impact amount on a drive wheel (e.g., Patent Document 3). In this proposal, a correction value with respect to a slip amount of the drive wheel is determined by using the determined estimate of the external force impact amount, and an accelerating signal to the motor is corrected with the correction value to determine a motor torque command value.